The present disclosure relates to a static eliminating device electrically discharging a photosensitive drum and an image forming apparatus including a plurality of photosensitive drums along a transfer belt.
An image forming apparatus of an electrographic manner may include a plurality of photosensitive drums along a transfer belt. A surface of each photosensitive drum is electrically charged and exposed according to image data, and thereby, an electrostatic latent image is formed. Moreover, the electrostatic latent image is developed by adhering each color toner, and thereby, each color toner image is formed. The color toner images respectively formed on the photosensitive drum are primarily transferred onto a transfer belt, and thereby, a full color toner image is formed. Further, the full color toner image is secondarily transferred onto a sheet.
In the image forming apparatus, at the time of primarily transferring, difference in inflow of transfer current between a toner adhesion portion and a toner non-adhesion portion of the photosensitive drum occurs and influences electrically charging performance of the photosensitive drum, and thereby, image failure due to a transfer memory may occur. If the transfer current is lowered, inflow of the transfer current to the photosensitive drum may be restrained, but it is feared that transfer failure occurs.
Thereupon, for example, the image forming apparatus includes a static eliminating light source (a static eliminating device) located between primarily transferring and cleaning with respect to the photosensitive drum to irradiate the photosensitive drum with static eliminating light, and thereby, to electrically discharge (to perform so-called post-transfer static elimination) the photosensitive drum. The static eliminating light source also may irradiate an adjacent photosensitive drum arranged at a downstream side in a rotational direction of an intermediate transfer belt with the static eliminating light to electrically discharge (to perform so-called pre-transfer static elimination) the adjacent photosensitive drum. Thereby, because electric potential of the photosensitive drum before primarily transferring is lowered, if transfer current is lowered, occurrence of image failure due to the transfer memory may prevented without causing transfer failure. Moreover, because one static eliminating light source is commonly used for the post-transfer static elimination and the pre-transfer static elimination of two adjacent photosensitive drums, it is not necessary to provide new static eliminating light source and cost reduction is actualized.
However, the above-mentioned static eliminating light source is composed of LED arrays having LEDs as a light source arranged along an axial direction of the photosensitive drum. Therefore, in order to bring both functions of the post-transfer static elimination and the pre-transfer static elimination, there are problems that respective specific LEDs directed to respective directions for the post-transfer static elimination and the pre-transfer static elimination are required and the number of LEDs is increased.
By contrast, for example, the image forming apparatus may apply a side-light type static eliminating system using a static eliminating part (a static eliminating device) having one LED (a light source) and a light guide body to bring both functions of the post-transfer static elimination and the pre-transfer static elimination. This light guide body includes a first reflecting part and a second reflecting part (two reflecting faces) along the axial direction of the photosensitive drum.
In the image forming apparatus, surface electric potential difference (e.g. surface electric potential difference between an exposed area and a non-exposed area) is often caused in the photosensitive drum before electrical charging step, and then, there is a problem that image failure, such as so-called drum ghost, occurs due to this surface electric potential difference. In order to restrain such image failure, the image forming apparatus may include a static eliminating device irradiating a surface of the photosensitive drum with static eliminating light before electrical charging step to electrically discharge surface electric potential of the photosensitive drum to a predetermined residual electric potential level. The static eliminating device may be configured to convert light from a light source to linearly spreading light by a light guide body and to expose the photosensitive drum.
For example, in the image forming apparatus, the static eliminating device is composed of a light guide at a process cartridge including the photosensitive drum and the light source at an apparatus body. The light guide is composed of a lens and an exterior case. In the lens, a plurality of V-formed grooves (prisms) are provided. The groove is formed at an angle of 5-15 degrees with respect to a radial direction of the lens.
As mentioned above, in the static eliminating device including the one light source and the light guide body, it is necessary to restrain non-uniformity of light quantity in the axial direction of the photosensitive drum between the static eliminating light for actualizing the pre-transfer static elimination and the static eliminating light for actualizing the post-transfer static elimination outputted from the light guide body. In order to restrain non-uniformity of light quantity of the static eliminating lights, it is required to greatly heighten accuracy of a shape of the reflecting face of the light guide body. The reflecting face of the light guide body is formed so as to arrange the plurality of prisms (grooves) along the axial direction. An emission angle of light emitted by reflection of the prism (light emitted from an emission face side) and an emission angle of light emitted from a back face of the prism by transmission through the prism without reflection are different from each other. Therefore, in the light guide body including the one reflecting face, because it is difficult to uniform light quantities of pre-transfer static eliminating light and post-transfer static eliminating light in the axial direction, the above-mentioned static eliminating device includes two reflecting faces in the light guide body. However, because a cost of metal mold for forming the two reflecting faces elongated in the axial direction becomes very expensive, a cost as a product unit price is increased.
Incidentally, with respect to the pre-transfer static eliminating light, if the light quantity is too small, sufficient effect preventing image failure of transfer memory cannot be obtained, and if the light quantity is too large, character scattering may occur to bring image degradation. Moreover, with respect to the post-transfer static eliminating light, if the light quantity is too small, static eliminating function is insufficient, and if the light quantity is too large, carriers due to exposing expensively may occur to bring occurrence of image failure of transfer memory. Therefore, it is necessary to uniform light both pre-transfer static eliminating light quantity and post-transfer static eliminating light quantity within a desired range over the whole area of in the axial direction, but it is very difficult to actualize desired pre-transfer static eliminating light quantity and pre-transfer static eliminating light quantity over the whole area of in the axial direction, particularly in the light guide body including the one reflecting face.
The light guide body of the static eliminating device as mentioned above needs to include an attachment shape for being attached to a drum unit or the like provided with the photosensitive drum. However, in the light guide body, because light may be leaked from a portion where this attachment shape is formed, non-uniformity of light quantity in an axial direction of the light guide body (in the axial direction of the photosensitive drum) may occur due to light leak depending on a position where the attachment shape is formed.
Moreover, the attachment shape may function as positioning of the light guide body to the drum unit or the like. However, depending on its shape and a positioning way, the static eliminating light quantity may vary due to variation of a distance between the light source and the light guide body. Further, non-uniformity of light quantity in the axial direction of the light guide body (in the axial direction of the photosensitive drum) may occur due to thermal deformation, such as curvature, by thermal expansion and thermal contraction of the light guide body.